Ments



W. T. BIRDSALL.

METHOD OF EXHAUSTJNG.

APPLICATION FILED MAY 4' I915.

1 ,3 1 8 832 v Patenred Oct. 14, 1919,

WITNESSESf INVENTOR Wilfred r Biro/50H. BY

Q a9. ATTORNEY container walls.

UNITED STATES PATENT oEEIoE.

wmEEEn '1. EIEDSALL, 0E MON'I'CLAIR, NEW JERSEY, Ass IeNoE, BY MESNEASSIGN- man, To wEsTINGH USE ELECTRIC 8: MANUFACTURING COMPANY, ACORPORA- METHOD OF EXHAUS'IING.

Specification of Letters Patent.

Patented Oct.14, 1919.

Application filed my 4, 1915. Serial No. 25,864.

To all whom it may concern:

Be it known that I, WILFRED T. BIRDSALL, a citizen of the United States,and a resident of Montclair, in the county of Essex and State of NewJersey, have invented a new and useful Improvement in Methods ofExhausting, of which the following is a specification.

My invention relates to the manufacture of vapor electric apparatushaving a highlyexhausted container of vitreous material, such, forexample, 'as a glass rectifier, and it has for its object to provide asimple, economical and effective method of removing deleterious gasesfrom the interior of the container during the exhausting process. Thesingle figure of the accompanying drawing is a side view, partially insection and partially in elevation, of a vapor arc rectifier, togetherwith attendant apparatus necessary for carrying out my invention.

It is well known that in the manufacture of vapor rectifiers and otherlike apparatus requiring a high operating vacuum, extreme difliculty isencountered in removing occluded gases from the inner surfaces of theWhile, at the conclusion of the pumping process, the device may indicatean extremely high vacuum, yet when the rectifier is put into operationand the walls arehighly heated, it is found that occluded gases aregiven or which tend to lower the vacuum to such a marked degree as toseriously impair the rectifier operation. In order to remove the gases,it has been customary in the past tohighly heat the container wallduring the process of ex hausting as, for example, by baking it in anoven or by assing current through the device while t e pump is stillconnected thereto. The oven treatment is not entirely satisfactory for,no matter how highly the oven may be heated, it is found that actualoperation will set free occluded gases even though heat, ,by itself,fails to do so. On the other hand, in the ordinary rectifier, ifsufiicient heat is generated by the passage of current between theelectrodes to satisfactorily drive off all the occluded gases, it isfound that such an amount of current is required as to seriously impairthe seals.

I have found that, by surrounding a rectifier with a medium having lessheat-absorbing capacity than that in which it is very high degree.

intended .to operate and by then passing current through the device, thewalls maybe so highly heated as to efi'ectually remove the occludedgases and, at the same time, such a small amount of current is necessaryfor the required heat that the seals are not afiected.

I find that, by operating a rectifier in theair which is to be normallyoperated in a liquid such, for example, as water or oil, I am able tosecure a vacuum of great permanence.

Referring to the accompanying drawings, a glass rectifier'bulb ofconventional type is shown at 1- and embodies a pair of mam (anodes 2and 3, a main cathode 4 and an auxiliary starting and maintaining anode5. Connection to a pump may be made by a suitable tubulature 6. Therectifiermay be started and maintained in operation by a small arebetween the anode 5 and the oathode 1, current being derived from anysuitable direct current source, such, for example, as a battery 7. Loadcurrent for the main anodes 2 and 3 is derived from a transformer 8 andmay be adjusted in voltage by suitable taps 9 and 10, and may beadjusted in amount by a suitable rheostat 11. The rectifier 1 isdesigned to be operated in a cooling fluid, as, for example, byimmersion in a tank 12. On account of the much higher heat absorption ofa liquid than of the atmosphere, the container 1 would be, heated tocollapse were it attempted to' run full-load current therethrough in theatmosphere. In the process of manufacture, however, I first exhaust thetube -1 in the ordinary manner and then pass current thereto from thesource 8 in such amounts as to heat the container to a The amount ofcurrent necessary for this operation is small, owing to the low heatradiation, and I am enabled to obtain a very high heating of thecontainer wall without using undue amounts of energy and withoutendangering the seals. At the same time, abnormally favorableelectrostatic conditions are rovided within the container 1 for the lieration of occluded gases.

With the above described process, the gas may 'be efl'ectively removedfrom the container walls, but the abnormally high vapor pressure causedby the'small heat-radiating capacity produces a stringing of the are andthe heating of the anodes only in small sharply defined spots. The nextste in the complete exhausting process is, in e ect, the converse ofthat above described. In order to heat the entire anodes thoroughly, itis necessary to provide an abnormally high vacuum and this result may beobtained by surrounding the rectifier with a medium of greaterheat-absorbing capacity than that employed in normal operation. If therectifier is designed to be submerged in the liquid of the tank 12,when, under normal load, the desired abnormal cooling may be provided byimmersing a cooling coil 14 in said liquid and by circulating brine or asimilar fluid therethrough. The vapor pressures within the rectifierwill then be reduced to an abnormally low amount, so that substantiallyall the current flow within the container takes place by currentcarriers originating at one terminal and passing to the other so that agreat share of the energy represented by the voltage drop within thedevice is delivered at the anodes, heating all portions thereof to ahigher degree than would be the case in normal operation and effectivelydriving ofi' the occluded gases therefrom. After the exhausting processhas been completed, the entire device may be left in the liquid of thetank 12 for normal operation and it will there, at rated load current,never be subjected to as severe treatment as that just described. Thevacuum will therefore be substantially unaffected by liberation ofoccluded gases during normal operation.

I may provide the conducting leads to the difierent electrodes withheavy insulating coatings 1313, as shown, in order to prevent shortcircuiting of the device and harmful electrolytic action if an operatingcooling medium of conducting material, such for example, as water, beemployed.

I have described my invention as applie to the air treatment of a bulbwhich is to operate under water, but I desire to have it skilled in theart that it is susceptible of Various minor changes and modificationswithout departing from the spirit thereof, and I desire, therefore, thatno limitations shall be placed thereupon except such as are imposed bythe prior art or are specifically set forth in the appended claims.

I claim as my invention:

1. The method of liberating occluded gases from the interior of apartially exhausted vacuum; type electric device by means of heatingcurrent transmitted thereinto through the working seals thereof -whichcomprises surrounding said device by a less effective heat-absorbingmedium than that in which it is designed to operate, passing currenttherethrough of substantially the same magnitude as the normal workingcurrent, and pumping out the liberated gases.

2. The method of providing abnormal gas-liberating conditions within thecontainer of a vacuum-type electric device by means of heating currentpassing through the Working-current path thereof, without overloadingthe seals thereof, which comprises operating said device in a mediumhaving less heat-absorbing power than that in which the device isdesigned to normally operate and passing substantially normal loadcurrent therethrough.

3. The method of heating a vacuum-type electric device to a gas-freeingdegree by heat electrically generated therein without unduly heating theleading-in conductors thereof, which comprises immersin said device in apoorer heat-absorbin me ium than that in which it is designe to normallyoperate and passing substantially load current therethrough.

4. The method of removing occluded gases from the electrodes of a vaporelectric device which comprises operating said device in a medium havinggreater heat-absorbing power than that in which it is designed tonormally operate, whereby the vapor pres sure will be abnormally loweredand all ortions of the anodes will be highly heate In testimony whereofI have hereunto subscribed my name this 28th day of April,

